I use the T/H on take off when towing my 14K fiver.The truck seems to like the shift pattern better.Once up to speed,about 50 mph,I'll shift out of T/H,and stay in 4th till the rpm drops down to around 1700-1750.
I have found that everything just purrs along at close to 2000 rpm,I "think"
my MPG may be a little better holding close to 2000 rpm
My 04.5 Dodge CTD 4 speed 48RE tranny has the 4.10 rear end,and at 2K rpm in 4th it is right at 65mph